Transitions and Zoning in Porphyry Epithermal Districts€¦ · Transitions and Zoning in...

Transitions and Zoning Transitions and Zoning in Porphyryin Porphyry--Epithermal Epithermal

Districts:Districts:

Indicators, Discriminators, Indicators, Discriminators, and Vectorsand Vectors

AMIRA Project Proposal AMIRA Project Proposal -- P765P765

El Teniente - Peripheral veins and argillic alteration

Porphyry-Epithermal Districts

Adapted from Sillitoe (1989)

• porphyry (Cu-Mo-Au) • epithermal (Au-Ag) • skarn (Cu-Au) • carbonate replacement

(Zn-Pb-Ag) • sediment-hosted (Au)

These districts host diverse styles of ore deposits and metal associations

Discrete mineralized zones in these districts(PCD, HS, LS, IS) are typically separated by barren gaps• We do not see continuity between deposit styles

• Hybrid mineralization styles are rare

Porphyry-Epithermal Districts

How can we identify productive ore zones within these large magmatic-hydrothermal systems?

Can we use peripheral deposits ± alteration systems to point us towards major deposits?

Rhodochrosite cement, phreatic breccia, Kelian, Indonesia

Example: Collahuasi, Chile

Landsat 741 /Spot merge

Volcan Irruputuncu

West Fissure/Quehuita Fm

Rosario DepositCollahuasi Fm

HS Vein - Cerro La GrandeLS Vein - Monctezuma

Example: Collahuasi

26 Mt fine Cu - Rosario PCD

Project Goals

We aim to help improve exploration success in porphyry-epithermal districts

Our goal is to develop and test criteria that will help explorers:• indicate prospective environments

• discriminate between mineralization styles and between productive and non-productive districts

• vector towards ore zones

qz-cp-cc stockwork, qz-fspr porphyry, Spence, N. Chile

Scope of Project

Four discrete research modules have been designed to address significant technical challenges within a given mineral district.

1. Lithocap domain2. Transitional environments3. Carbonate environments4. Alkalic systems

The modules that will be included will depend on sponsor interest and access to suitable sites

Volcanic Fumarole, White Island, New Zealand

Module 1: The lithocap domain

Challenges for exploration:• diversity of possible

origins• difficulties assessing

location of and depth to mineralized zones

• deposits may be laterally offset from alteration domains

• Can we systematically track alteration, metals, ± physical properties as a pathfinder to ore?Modified from Sillitoe

(1995)

Module 2: The transitional environment

Cadia Ridgeway: Late cp-epi-py veins with broad orthoclase alteration selvages

Kelian: sphalerite-galena-carbonate-

cemented auriferous breccia

The significance of green rocks:• When does the presence of

chlorite or epidote indicate proximity to a large hydrothermal system?

• Can we discriminate between green rocks on the margins of a porphyry centre from those around epithermal veins?

• Can we discriminate background alteration (diagenesis, metamorphism)?

Bingham Canyon

Module 3: The carbonate environment

• What happens to metals and fluids as they migrate through sedimentary rocks away from porphyry intrusions?

• What is the nature and extent of alteration in these environments?

• What is the nature and significance of zonation around carbonate-hosted-HS systems?

Barney’s Canyon: laminated

dolomitic siltstone

Module 4: Alkalic Systems

1 km

LS alkalic epithermale.g. Ladolam, Porgera, Emperor

porphyry Au-Cue.g. Ridgeway, CFE, Mount Polley

proximal Cu-Au-Fe skarne.g. Big Cadia

Alkalic porphyries are poorly understood relative to calc-alkalic systems

• alteration zonation?• carbonate zonation?• peripheral deposits?• lack of HS systems?

Potential Study AreasWe need to target districts with known and well-constrained

porphyries and peripheral systems

Collahuasi

Farrallon Negro, El Teniente

Lepanto FSE

Module 1

Batu Hijau

Module 2

Bingham

Cadia

Module 3

Oyu Tolgoi

Module 4

Palinpinon

Barren System

Under Cover Exploration

The Cadia district of Australia is one the largest known alkalic porphyry Au-Cu districts

It contains four known porphyry mineral centres (two of which have preserved tops),

Peripheral skarns and barren high-level alteration zones are exposed at surface, and also by mining and exploration drilling.

Cadia Quarry: pegmatitic or-qtz-bio-py-mo-cp cemented breccia with sericite-altered QMP clasts

Cadia Far East: albite-chlorite alteration overprinting bio-cp

Cadia District, NSW, Australia

Cadia District, NSW, Australia

Jensen & Barton (2000)

Galore Creek

Goonumbla

Silurian cover

Cadia Far East Little Cadia

500 m

21,000 mN 22,000 mN

5,500 mRL

5,000 mRL

23,000 mN

P1Fault

P2Fault

CB

FaultZ one

Regional Propylitic (chl-carb-epi-hm)

Skarn (py-hm-mt-chl-carb-gt)

Skarn Propylitic (epi-py)

Albite-Sericite (ab-qz-ser-py-tm)

Sodic (ab-qz-hm)

Calc-Sodic (ab-act-qz-carb-py)

Inner Propylitic (ab-chl-act-epi-qz-cp-lm-pr-mt-hm)

Legend - Alteration

Outer Calc-Potassic (ab-chl-act-epi-Kf-bn-mt-hm-cp)

Inner Calc-Potassic (ab-bi-Kf-act-qz-mt-bn)

4,500 mRL

After Tedder et al. (2001)

Palinpinon is a barren, porphyry-related system exposed over a 3 km vertical interval.

Alteration assemblages:K-silicate (biotite, magnetite)calc-silicate (garnet, clinopyroxene)hypogene advanced argillic (andalusite, zunyite)Steam-heated advanced argillicpropylitic (tremolite-actinolite, epidote) illitic (smectite, illite)

There are fossil (0.9 Ma) PCD-HS mineral assemblages, and recent PCD-LS assemblages

Bladed alunite, Palinpinon geothermal field, Philippines

Palinpinon geothermal field, Philippines

Palinpinon geothermal field, Philippines

Alteration zonation & overprinting relationships - Palinpinon (Rae, 2002)

Other Suitable Districts

High base level knowledge

Batu HijauCollahuasiEl TenienteLepanto - Far South EastFarellon NegroTintaya / Antapaccay

From Hedenquist et al. (1996)

Our objectives can be grouped into three themes:

Research Objectives

Grasberg:quartz-magnetite stockwork

• Indicators

• Discriminators

• Vectors

These will be based on fundamental geological documentation of the selected districts

• What makes a given mineral district prospective for porphyry/epithermal mineralization?

• Many factors need to be considered, involving processes that operate at a variety of scales.

• We aim to define the diagnostic geological, geochemical and geophysical charactersitics of prospective districts

Indicators

Steam-heated advanced argillic alteration, El Indio – Pascua district, Chile

DiscriminatorsCertain minerals can be used to discriminate effectively between deposit styles and/or alteration zones (e.g., garnet, amphibole, pyroxene, alunite)

We will test the potential of other minerals to better discriminate between the various hydrothermal environments, e.g.:

• Sphalerite • Kaolinite / illite• Pyrite • Epidote / chlorite• Enargite • Carbonates• Apatite • Biotite

These tools may be able to help assess the depth of erosion, and thereby help to evaluate the potential for shallow and/or deeper-level ore deposits

Collahuasi: Late-stage massive sulfide veins

Mineral Discriminators: Module 1

Example: Alunite REE fractionation

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu0.01

0.1

1

MH alunite (WR alteration)Syn-Au MH aluniteSteam heated alunite

Alun

ite R

EE

(nor

mal

ized

to h

ost r

ock

com

posi

tion)

Data from El Indio-Pascua Belt (Deyell, 2001)

Mineral Discriminators: Module 2

Example: Epidote

0.01

0.1

1

10

100

1000

0.001 0.01 0.1 1.0

Y/Sr

Cu/E

u

El TenienteCollahuasiRio BlancoN ChilevolcanicsBasalt standard

PCD’s

Volcanics

HS

Data from Chile PCDs (Cooke, 2001)

Vectors

We will develop geological and whole rock and mineralgeochemical vectors that can be used to help identify the mineralised centres

These will be based on the characteristics and geochemistry of vein arrays and alteration zones

Low sulfidation epithermal Au-Ag veins, Serijan Pit, Mt Muro, Indonesia

Zn-rich Polymetallic VHMS DepositsZn-rich Polymetallic VHMS Deposits

VV

VV

VV

VV

V

V

Increase of Eu*in Fe-Si cherts

δ34S decreasesδ18O decreases

limit of Na depletionCCPI increases

Alt index increases

S/Na2O increases

Mn content ofcarbonate increase

Limit of Tl haloBa/Srincreases Tl, Sb

increase

Hangingwall volcanic facies

Ore equivalent facies

Massive Zn-Pb-Cu sulfide

Footwall volcanic faciesV

Silica zone (qtz-chl-ser-py)

Chlorite zone (chl-ser-py)

Carbonate zone (carb-chl-ser-py)

Sericite zone (ser-carb-chl-py)

Albite zone (alb-qtz)

ALTERATION

Methodology

Starting point: well-constrained geology & geochronology

Modules 1 & 4: mineralogy & mineral chemistry, petrography, stable isotopic and exploration geochemistry & geophysics

Modules 2 & 3: also require fluid inclusions for depth constraints

We will carefully assess features that have the potential to offer simple, field-based criteria for determining where we are in the system

Spence, N Chile: biotite altered andesite; qz-cp veins cut by qz-py-chl vein with sericite alteration halo

Research TeamProject Leaders

David CookeBruce Gemmell

Chief InvestigatorsCari DeyellRobina SharpeNoel White

Cadia Hill Monzonite with qz-epi-bn-cc vein, Cadia Hill

Potential Collaborators

Jeff HedenquistDick TosdalBrian TownleyPeter Hollings

Timetable

Year 1• Literature review complete• First year mapping & logging results• Pilot studies on selected minerals completed• Initial GIS compilation completeYear 2• Bulk of geochemical analyses complete• Palinpinon study complete• Preliminary geochronology & fission track• Petrographic study of textural discriminators

completeYear 3• Final synthesis of all field and analytical data• Final district-scale analysis• Comparative study complete• Final development and testing of geochemical

vectors

Milestones

Goonumbla: Apatite inclusions in anhydrite phenocryst

DeliverablesDeliverables

Geological and geochemical vectors to identify the

location and likely distance to high-grade ore zones

Deliverables

• New mineral discriminators for different hydrothermal environments

• Criteria for evaluating a district’s potential

• A database of geochemical, geological, and geophysical data for the selected mineral districts

Electrum, tellurides & base metal sulfides, Acupan, Phillipines

Key Items• Salaries (Deyell, Sharpe)• Analytical• Travel• Reporting

Summary• AMIRA Funding - $225K p.a. • ARC Linkage - $225K p.a.• In-kind (CODES) ~$100K p.a.• Additional funding streams also being

pursued (e.g., NSERC)• Industry Leverage ~ 22 : 1

Budget

SponsorshipWe are seeking $25K AUD (~$14K US) per annum from each sponsor for 3 years

Preferred sponsorship -nine companies + ARC

(full budget) = 2-3case studies +barren system

Minimum sponsorship -four companies + ARC (= 1 district + barren system)